[quote=@AndyC]
<Snipped quote by Sep>

This is one of those questions that they've come up with a bunch of different answers for, like the old "how come nobody recognizes Clark Kent is just Superman with glasses on" routine.  In the Golden Age it was stated that his hair and nails just sorta stop growing at a certain length.  The explanation that John Byrne used (and the one that [@Lord Wraith] mentioned) was that he bounces Heat Vision off of a mirror-- or, more accurately, a reflective piece of his Kryptonian spaceship that wouldn't just melt when he laser-eyes it.

The explanation that [i]this[/i] version of Superman is using is that he can extend his gravitational field around anything he touches, temporarily imparting his own invulnerability onto anything or anyone in direct contact with his body.  This would be how he can lift heavy objects without them collapsing under their own weight, how he can punch someone without their head splattering into a fine mist, how he can be intimate with Lois without accidentally tearing her to pieces, and for mundane purposes, how he can shave or cut his hair and/or toenails without destroying the clippers.  I'd also mention that since hair and nails are effectively dead cells once they grow past a certain point, as soon as they're outside of Clark's invulnerability field they no longer possess his durability, so you couldn't, say, fashion some really gross weapon out of Superman's indestructible toenail clippings.
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Damn it. Toe nail man isn't going to be a thing now.